Magnetic storage systems, such as a hard disk drive (HDD), are utilized in a wide variety of devices in both stationary and mobile computing environments. Examples of devices that incorporate magnetic storage systems include desktop computers, portable notebook computers, digital versatile disc (DVD) players, high definition television (HDTV) receivers, vehicle control systems, cellular or mobile telephones, television set top boxes, digital cameras, digital video cameras, video game consoles, and portable media players.
A typical HDD includes magnetic storage media of one or more flat disks. The disks are generally formed of two main substances, namely, a substrate material that gives it structure and rigidity, and a magnetic media coating that holds the magnetic impulses or moments that represent data. A typical HDD further includes a read/write head, generally a magnetic transducer which can sense and/or change the magnetic fields stored on the platters. The read/write head is attached to a slider, generally an armature capable of placing the read/write head at a desired location over the platter. In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by a suspension, such that, optimally, a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk.
The height of the read/write head over the disk is referred to as the “fly height.” The fly height of a HDD is a critical distance. If the fly height is too high, the magnetic fields will be too weak or dispersed for the read/write head to function. If the fly height is too low, there is an increased danger of a “head crash,” wherein the read/write head touches the surface of the magnetic storage medium, thereby destroying data and/or damaging the read/write head or the magnetic storage medium. Moreover, as the density of data on the magnetic storage medium increases, the strength of the magnetic fields generally decrease, in order to minimize interference. Higher areal density in magnetic storage medium generally requires both advanced read/write transducer design and very fine control of the fly height of the read/write head. Additionally, magnetic storage media are frequently subjected to various magnitudes of mechanical shock as a result of handling. As such, performance and design needs have intensified. Additionally, small drives have very narrow tolerances. Disk drive heads and sliders are designed to fly in very close proximity to the disk surface. In some systems the head may be designed to fly three to five nanometers above the disk surface.
Accurate measurements of the spacing between the read and/or write head and the disk surface is a necessity in any HDD design to verify the head-to-disk interface functionality for mechanical, tribological and electrical performances. Further, detection of contacts of a head and a disk is useful for a number of diagnostic tests, enabling assessments such as component-level fly ability and durability, drive-level reliability, and production-level screening to be made, as well as for providing input to fly-height calibration and adaptive fly-control systems that enable dynamic adjustment of flying height in disk drive systems.